Pipes are one of the most important equipment in a boiler. Repairing leaks in boiler pipes requires a lot of time and high maintenance costs. Therefore, pipe damage to the boiler must be repaired immediately and prevented, so that it does not occur. Leaks in pipes are due to a material's lack of resistance in withstanding fluid pressure and thinning of thickness, so this research uses microstructure testing to determine the content of a material. From the test results obtained perlite pipes that leaked 48% and pipes that did not leak 31.5%, while the results from ferrite pipes that leaked were 43.5% and pipes that did not leak 35%. So, the pipe leaking level is based on the microstructure of the embedded pipe samples. without leaking, the result was that the pearlite content was 31.5%, while the ferrite content was 35%, so it could be concluded that the steel content was soft and the gran size or granular phase microstructure value was 7.24071. In the microstructure of the leaked embedded pipe sample has a pearlite content of 48%, which is higher than the pearlite content, compared to a ferrite content which is lower than pearlite with a value of 43.5%, so that the steel has a fairly high level of hardness, which is caused by pearlite, and obtained a gran size or granular microstructure phase value of 5,9039.